Ash melting furnace and ash melting method thereof

ABSTRACT

The object of this invention is to provide an ash-melting furnace which can respond to fluctuations in the load and which will be capable of highly efficient and stable operation. In an ash-melting furnace which heats and melts the primary ash and the fly ash obtained by combustion together, this invention is characterized by supplying the primary ash (ash containing rough particles) from upper end of the furnace to form an upper layer of a two-tiered layer of ash, supplying the fly ash (ash containing minute particles) from an upper end of the furnace to form a lower layer of the two-tiered layer of ash, moving the two-tiered layer together towards the far end of the furnace, and heating and melting the two-tiered layer by a burner to form molten slugs during the moving step. When the burner is an oxygen-enriched burner, this configuration makes it possible to control the volume of oxygen to be added to the burner air (including changing the density of the oxygen). This invention can control not only the volume of fuel but also the density of the oxygen-enriched air and the volume of the ash to be supplied in response to the state of flow of the molten ash melted by the oxygen-enriched burner.

FIELD OF THE INVENTION

This invention concerns an ash-melting furnace and a method used to meltthe ash. The furnace uses a burner to heat and melt the surface of ash,which may be the fly ash or the ash exhausted from an incinerator suchas that which burns municipal garbage or industrial waste, or from acoal-fired boiler. This melted ash is then discharged as liquifiedslugs.

DESCRIPTION OF THE RELATED ART

The material exhausted from an incinerator which burns municipal garbageor industrial waste contains ash and exhaust gases. The ash is treatedwith a water-sealing process; the resultant wet ash is collected, anddry ash is collected in the dry state. The two types of collected ashare preprocessed by crushing them and magnetically separating andremoving their iron component which has a high melting point. The wetash is then put through a drier and mixed with the dry ash to formprimary ash.

The fly ash is captured when the gases exhausted from the incineratorpass through a dust chamber, such as a bag filter, before being releasedinto the atmosphere.

The fly ash contains a considerable volume of heavy metals and saltswith a low boiling point, and most of the components will volatilize anddisperse among the gases when the ash is subjected to thermal processingat high temperatures. However, the salts will damage the heat resistantportions of the furnace. This is why it is uncommon to melt the fly ashby itself. Rather, most ash processors mix the fly ash with the primaryash and melt them together.

To melt and solidify the ash mixture described above, a burner-styleash-melting furnace is used. This is a furnace which applies heat to thesurface of the ash to melt it and discharges the melted ash as slugs.There are two types of burner-style ash-melting furnaces: a furnace witha round, rotating surface, and a furnace with a fixed surface, which isan inclined reflecting furnace. Then following discussion ofburner-style ash-melting furnaces, the primary application for thisinvention, will be based on the latter type of furnace, a fixed-surfaceash-melting furnace, the operation of which will now be brieflyexplained.

FIG. 19 shows a fixed-surface melting furnace. In this drawing,ash-melting furnace 51 is comprised of floor 55, which inclinesdownward; ash supply unit 53, which is above one end of the main body ofthe furnace; discharge port 57, which is on the other end of thefurnace; fixed burner 52, which is installed on ceiling 56; and pusher58, which is a means to propel the ash forward in the furnace.

The supply unit 53 comprises ash stack 60 and its supply port 54. Ashstack 60 contains ash mixture 50, a combination of primary ash and flyash. The ash is fed by gravity to the highest surface of the floor ofthe furnace, directly below supply port 54. The ash mixture which dropsto this surface is intermittently forced along floor 55 towards theinterior of the furnace by the action of pusher 58. This forms a layerof ash 59 all along the inclined surface of floor 55.

The burner 52 is placed along the central axis of ceiling 56. Liquidfuel which is forced into the burner is atomized by compressed air orsteam from a waste heat boiler and sprayed into the chamber, where it ismixed with hot air supplied at the same time, causing it to combust. Theflames from the fixed burner 52 heat and melt the surface of ash layer59.

The end of floor 55 at the port 57 leads to the region where the flamesfrom the burner 52 radiate. The exterior surface of ash layer 59, whichcontinues to move towards the discharge port 57, is heated andliquified, forming molten ash 25, which collects in slug reservoir 65.This ash passes through drain port 20 in dike 23 as molten slugs 25 a,which drip out of discharge port 57. These slugs are carried on awater-sealed conveyor (not shown) and discharged to the exterior.

Related art designs for such an ash-melting furnace have the followingshortcomings.

The first problem has to do with the use of a burner relying on air.

If an air-fed burner is used in the related art apparatus describedabove, a preheater is needed to heat the air to be used for combustionin order to boost the temperature of the flame. Further, a dustseparator is needed because a large volume of the exhaust gas willconsist of substances with low boiling points. And NOx will be generatedfrom the nitrogen in the considerable quantity of air used forcombustion. For these reasons a recent trend is to substituteoxygen-enriched air (with an oxygen concentration of around 30%) forambient air (with an oxygen concentration of around 21%).

However, the ash to be melted in this sort of furnace consists ofvarious materials with different characteristics due to their differentcompositions. Insofar as incinerator ash is used, there is no way toavoid fluctuations of the load. The current demand is for appropriatecountermeasures for these load fluctuations to assure stable andefficient operation and to produce high-quality molten slugs.

The second problem is associated with slug reservoir 65, in which themolten ash 25 accumulates, and drain port 20, which extends through dike23 on the outlet side of the reservoir.

Dike 23, which creates the slug reservoir 65, and drain port 20 in dike23 are shown in FIG. 21. Slug reservoir 65 is a more or less rectangularcistern. The molten ash 25 which accumulates in rectangular reservoir 65is evacuated via drain port 20 in the center of the dike. However, themolten ash 25 which finds its way into the corners where dike 23 meetsthe walls of the reservoir stagnates there. The stagnant portions of theash experience a drop in temperature and become larger, thus narrowingthe channel. This has an adverse effect on the fluidity of the slug.

The third problem concerns the configuration of pusher 58, which movesalong floor 55.

Either the ash layer 59 falls naturally from supply port 54 of the ashstack 60 and immediately forms a layer of ash with an angle of repose γ,or the ash 50 from stack 60 is pushed towards the discharge port 57 onthe far end of the furnace by pusher 58, which moves along the floor 55at the entrance to the chamber.

Burner 52, which heats and melts the ash, is located along the centralaxis of ceiling 56. As can be seen in FIG. 22 (A), this burner creates amore or less round region of radiated flame 35 on the central axis ofthe surface of ash layer 59. The ash in heated region 35 a on theperiphery of region 35 is heated and melts, forming a well of moltenash. From the well, the molten ash 25 drips out of discharge port 57.However, as can be seen in FIG. 22(A) and FIG. 22(B), the pusher 58 usedin the related art has a pushing element made as a square form 58 a ofthickness t with a rectangular cross section. When the related artpusher 58 is used, the ash is pushed across the entire width of floor 55equally and uniformly.

Thus the ash is supplied to the region outside heated area 35 a in thesame quantity as it is to area 35 a. The ash supplied to the regionoutside heated area 35 a is pushed from supply port 54 towards dischargeport 57 in an unmelted state. This unmelted ash will be mixed in withthe melted ash 25 which drips out of discharge port 57, degrading thequality of slugs 25 a.

The fourth problem concerns the kinds of incinerator ash to beprocessed.

In addition to the aforesaid problem, related art ash-melting furnacesexperience the following problems concerning the supply of ash even whenonly a single sort of ash is to be melted.

1) When the ash is supplied to the entrance of the chamber on the nearend of floor 55 from stack 60 of ash supply unit 53, it is allowed tofall by its own weight. However, as the ash falls, it frequentlydevelops cross-linkages, making it impossible to produce an even supply.

2) The ash which falls onto the near end of floor 55 is pushed along theinclined surface of the floor towards discharge port 57 on the oppositeend of the chamber by pusher 58 to form ash layer 59. Pusher 58 movesback and forth intermittently. This intermittent movement, combined withthe absorbed impact of ash falling on clumps of ash particles with evena weak coupling index, can cause sudden undulations in the surface ofash layer 59. Thus the state of the ash surface heated and melted by theradiant heat from the flame of burner 52 is unstable, making itvirtually impossible to achieve a stable continuous outflow of moltenash 25.

In general, if different types of ash are to be melted, there will beanother problem. The ash 50 is supplied via the supply unit 53. Thesurface of ash layer 59, which is formed by the action of pusher 58 asit travels along floor 55, will come to rest at a different angle ofrepose γ with respect to floor 55 depending on what type of ash it is.With some types of ash, the leading end of ash layer 59 will come to astop a considerable distance from discharge port 57, or it will bepushed even beyond discharge port 57. If it stops too soon, the moltenash 25 will be formed short of discharge port 57, and its leading endwill not go the required distance even when propelled by pusher 58. Themolten ash 25 will not be able to flow out of the furnace, and it mayhappen that the heat-resistant material on floor 55 just beforedischarge port 57 becomes exposed and corrodes from the excessive heat.

If the ash layer travels too far, it will continue to melt, and whenpusher 58 moves as the molten ash 25 flows from the far side of floor55, the momentum of the new ash 50 which is supplied may cause themolten ash 25 to avalanche. Unmelted ash 50 will flow out with themolten ash 25, and the quality of the molten ash will suffer.

In other words, the angle of repose can be a help only when a stablesupply of ash is achieved, as discussed above. How to achieve a stablesupply of ash in the furnace is, therefore, a topic of the highestpriority.

There is a further problem. A mixture of primary ash and fly ash issupplied to the interior of the furnace via the ash supply unit 53 inash-melting furnace 51. A layer of composite ash is formed, heated andmelted.

However, an ash layer 59 which consists of this sort of compositemixture has the following problem. When the radiant heat from the flameof burner 52 is applied to its surface to heat it, the combustion gasesfrom the burner cause superfine particles such as the fly ash to beblown up and around. Many of these particles escape from the ash-meltingfurnace with the exhaust gases.

SUMMARY OF THE INVENTION

The object of this invention is to provide an ash-melting furnace whichcan respond to fluctuations in the load and which will be capable ofhighly efficient and stable operation. More specifically, its object isto provide an ash-melting furnace which is able to control the quantityof ash supplied and the quantity of heat produced by the burner inresponse to the state of the outflow of the molten slugs.

Another object of this invention is to provide an ash-melting furnacewith an efficient drain which can maximize the fluidity of the moltenslugs being released. More specifically, this object is to provide anash-melting furnace which will assure that the molten slugs consistingof molten ash which has accumulated in the slug reservoir will havesufficient fluidity to allow them to reach the discharge port and willflow at a higher velocity.

Yet another object of this invention is to provide an ash-meltingfurnace in which the pusher to force the layer of supplied ash along thefloor of the furnace towards the discharge port will have a pushingelement of a novel shape, so that as little as possible of the ashpushed forward by the pusher will land outside the region of the furnacewhere heat is applied, i.e., out of the region where the heat from theburner flame radiates.

Yet another object of this invention is to provide an ash-meltingfurnace having a configuration which enables a continuous stable supplyof ash from the supply port towards the discharge port in the floor ofthe furnace in order to assure a stable outflow of molten ash withminimum fluctuation.

Yet another object of this invention is to provide an ash-meltingfurnace and a method of melting the ash which will enable ash to bemelted efficiently when a composite ash consisting of a mixture of theprimary ash, namely, incinerator ash, and fly ash is melted. It will doso by preventing the fly ash from flying about in the furnace when thecomposite ash is melted.

The invention in claims 1 and 2 concerns control of the heating using anoxygen-enriched burner. It enables the control of the volume of oxygento be added to the burner air (including the ability to change thedensity of the oxygen). This invention can control not only the volumeof fuel but also the density of the oxygen-enriched air and the volumeof the ash to be supplied in response to the state of flow of the moltenash melted by the oxygen-enriched burner.

In an ash-melting furnace according to the invention in claim 1, whichcomprises an ash supply port to supply ash provided at one end of thefurnace; a slug discharge port to discharge the molten slugs of the ashat the other end of the furnace; an oxygen-enriched burner to melt theash supplied from the ash supply port, the supplied ash being pushedforward along an inclined floor towards a drain port provided at the farend of the inclined floor to drain the molten slug, this ash-meltingfurnace is characterized by the following features. It further comprisesa monitoring means to monitor the drain state at the slug drain port,such as a temperature, a volume, and a drain velocity of the continuousoutflow of the molten slug; and a control means to control either thequantity of the ash supplied or the quantity of heat produced by theoxygen-enriched burner in response to a signal from the monitoring meansin order to achieve a stable continuous outflow of the molten slug.

To be more specific, as claimed in claim 2, the ash-melting furnace hasa combustion control device which comprises a monitoring means tomonitor the drain state at the slug drain port, such as temperature,volume, and drain velocity of the continuous outflow of the molten slug;a calculation means to calculate a control signal either for thequantity of the ash supplied or the quantity of heat produced by theoxygen-enriched burner; and a control means to control either thequantity of ash supplied, or the quantity of heat produced by theoxygen-enriched burner in response to the control signal from thecalculation means.

This invention enables a reduction of the volume of NOx generated in thefurnace by properly adjusting the volume of oxygen supplied to theoxygen-enriched furnace, thus reducing the volume of thermal NOx to bereleased.

When the volume of exhaust gas is reduced, preheaters, dust eliminatorsand equipment to treat exhaust gas in order to eliminate NOx can be madesmaller, saving space in the plant or reducing its size as well. Byresponding to the state of discharging the molten slug from the slugdrain port, the furnace can be operated in a more stable and efficientfashion.

In this embodiment, if the detected temperature of the slug isappropriate, its volume of flow as calculated from the width and thevelocity of the slug flow can be adjusted by controlling the quantity ofash to be supplied, and the temperature and the velocity of the slugflow can be adjusted by controlling the quantity of heat produced by theburner.

The heat produced by the oxygen-enriched burner is controlled byadjusting the quantity of fuel supplied to the burner, the volume of airused to induce combustion, or the volume of oxygen added to this air.Thus a smaller volume of gas is required, and the temperature of thecombustion gases will increase rapidly. Less exhaust gas will bereleased and the temperature of the flame can be increased quickly. Thisallows combustion to be induced more efficiently.

The quantity of fuel, the volume of air, and the volume of oxygen arepreferably controlled independently.

In this invention, an infrared CCD camera monitors the drain state atthe slug drain port; the temperature, the volume, and the drain velocityof the continuous outflow of the molten slug are detected in respondingto these detected data; the quantity of the ash supplied and/or thequantity of heat produced by the oxygen-enriched burner are adjusted.Therefore, if the detected temperature of the slug is appropriate, itsvolume of flow as calculated from the width and the velocity of the slugflow can be adjusted by controlling the quantity of ash supplied, andthe temperature and the velocity of the slug flow can be adjusted bycontrolling the quantity of heat produced by the burner.

The heat produced by the oxygen-enriched burner can be controlled byadjusting the quantity of fuel supplied to the burner, the volume of airused to induce combustion, or the volume of oxygen added to this air.Thus a smaller volume of gas is required, and the temperature of thecombustion gases will increase rapidly if compared with theconfiguration with a conventional air burner which adjusts them byincreasing the volume of fuel and combustion air. With the configurationaccording to this invention, less exhaust gas will be released, and thetemperature of the flame can be increased quickly. Thus, this inventioncan provide an ash-melting furnace which can respond to fluctuations inthe load and which is capable of highly efficient and stable operation.

The object of this invention according to claims 3 through 5 is toprovide an ash-melting furnace with an efficient drain which maximizesthe fluidity of the molten slugs being released. In an ash-meltingfurnace according to the invention in these claims, which comprises anash supply port to supply ash provided at one end of the furnace; a slugdischarge port to discharge the molten slugs of the ash at the other endof the furnace; an oxygen-enriched burner to melt the ash supplied fromthe ash supply port, the supplied ash being pushed forward along aninclined floor towards a drain port provided at the far end of theinclined floor to drain the molten slug, this ash-melting furnace ischaracterized by the following features. It further comprises a guidewall on a dike for providing a fluidity of the molten slugs at the drainport.

To be specific, the guide wall of the dike preferably is continuallystraight or curved, and its width is gradually narrowed in a planesurface towards said drain port. It is also preferable that the drainport is provided in the center of the dike, and a floor of a slugreservoir is recessed along the orthogonal direction of the slug flow,which slopes gradually downward from upstream to downstream.

In the invention claimed in claims 3 through 5, since the guide wall isprovided on the dike at the end of the slug reservoir to pool the moltenslug, the ash melted by the heat from the burner is made to move towardsthe drain which is the outlet of the slug reservoir without beingcollected in a specially constructed reservoir unit and without leavingunburned sediment behind. The molten ash is efficiently directed towardsthe slug drain port, so that it can be discharged smoothly.

Because the slug reservoir is shaped like a funnel from its entry to itsdrain, the two corners on the sides of the dike are eliminated, and theflow of molten slug is now concentrated naturally towards the drain. Theflow velocity in the streamlined reservoir towards the dike is slowerthan in related art reservoirs. As a result, the heat-resistantmaterials near the dike experience less high-temperature corrosion.

Since the slug drain port is arranged directly in the center of thedike, the ash molten by heat from a burner installed along the centerline of the furnace body is assured that the central portion of themolten ash will flow smoothly along the center line of the floor.

The end of the floor inclines somewhat gradually downward along itscenter line to form a concavity. This assures that the flow of moltenash towards the drain can be directed and concentrated in the directionof the drain even from locations distant from the drain.

The notch of the drain port may also be shaped like the bottom of aship, so that the molten slug will move smoothly while passing throughthe drain.

In an ash-melting furnace according to the invention in claims 6 through8, which comprises an ash supply port to supply ash provided at one endof the furnace; a slug discharge port to discharge the molten slugs ofthe ash at the other end of the furnace; and a pusher to push the ash onthe inclined floor supplied from the ash supply port towards the regioncovered by the radiant heat of a burner for melting the ash, thisash-melting furnace is characterized by the following features. Thepusher mentioned above has a pushing surface provided at the endthereof, and the shape of either side of the pushing surface isdifferent from the shape of the central portion of the pushing surfacein order to supply the ash efficiently to the central region covered bythe radiant heat of the burner.

The central portion of the pushing surface can be higher than eitherside, or the center portion can be formed flat and either side can havea backwardly inclined surface in order to supply the ash efficiently tothe central region covered by the radiant heat of the burner.

As an alternative, the central portion of the pushing surface can dropaway towards the center to form a concave pushing surface so that thepushing surface is directed towards the center line which passes throughthe middle of the region of radiant heat.

Since a pusher whose front end is configured as in this embodiment isquite different from pushers of the related art, which had a rectangularcross section and which pushed a uniform quantity of ash all acrosstheir width, this new design allows a larger quantity of ash to bepushed towards the center of the furnace. This maximizes the quantity ofash supplied to the center and minimizes the quantity supplied to eitherside.

If the end of the pusher has its sides furthest forward with the surfacedropping away towards the center to form a concave pushing surface, theash pushed by the said surface will be directed towards the center linewhich passes through the middle of the region of radiant heat. Thisdesign has the effect of maximizing the quantity of ash delivered to thecenter of the furnace and minimizing the quantity delivered to eitherside.

Since the central portion of the pushing surface is higher than eitherside, or the center portion can be formed flat and the both sides areraked back at a steep angle, the advancing pusher will leave behind theash on either side which is outside of the heated region comprising thearea covered by the radiant heat from the burner in the center of thefurnace. When the pusher advances, the ash in front of its centralportion will be pushed forward, but the ash on either side of itsbackwardly inclined surfaces will be left behind. This design makes itpossible to supply ash only to the center of the furnace.

Since the end of the pusher has its sides furthest forward with thesurface dropping away towards the center to form a concave pushingsurface, the ash pushed by the surface will be directed towards thecenter line which passes through the middle of the region of radiantheat. This design has the effect of maximizing the quantity of ashdelivered to the center of the furnace and minimizing the quantitydelivered to either side.

The embodiments defined in claims 9 through 11 show ash-melting furnacesfrom which the drainage of molten ash is stable with little fluctuation.In an ash-melting furnace comprising an ash supply port to supply ashprovided at one end of the furnace; a slug discharge port to dischargethe molten slugs of the ash at the other end of the furnace; a burner tomelt the ash supplied from the ash supply port, the supplied ash beingpushed forward along an inclined floor towards a drain port provided atthe far end of the inclined floor to drain the molten slug, thisash-melting furnace is characterized by the following features. Itfurther comprises an ash feeding means, such as a screw feeder, providedin the ash supply port to continuously feed the ash from the ash supplyport along the inclined floor.

The first ash feeding means is preferably oriented lengthwise along theinclined floor from the ash supply port, and the second ash feedingmeans is oriented vertically above the ash supply port. It can furthercomprise a gate along the wall of the ash supply port in order to adjustthe height of the layer of ash on the inclined floor.

With this invention, since the ash delivered via the supply port ontothe floor of the furnace is continuously pushed forward along the floorby the feeding device, the layer of ash created on the inclined surfaceof the floor will travel forward in a stable fashion withoutexperiencing undulation. It will be in a uniform state, and its surfacewill receive a constant quantity of radiant heat from the burner. Thiswill produce a stable drainage of molten ash. Because the feeding deviceis a screw feeder, the ash can be supplied continuously or in varyingamounts. This allows the system to respond effectively to loadfluctuations due to the type and condition of the ash used.

Since the screw feeders are provided to supply the ash both from thesupply port to the near end of the furnace floor and from there down thefloor to the far end, these feeders allow the quantity of ash suppliedto be varied across the width of the furnace.

If a plurality of screw feeders are installed across the width of thefloor and the quantity of ash to be supplied is controlled, they allowheating disparities across the width of the furnace which are due to theposition of the burner to be addressed by increasing or decreasing thequantity of ash being fed. This allows the state of melting to beequalized across the furnace.

The feeding means to continuously feed the ash along the floor willcreate a stable ash layer. If a gate is also provided at the supply portto change the height of the partition which forms the supply unit, itcan be used to control the angle of repose of the ash layer. This willassure a stable drainage even when ash of different types is beingmelted.

The invention claimed in claims 12 through 17 concerns an ash meltingfurnace which mixes and melts the primary ash and the fly ash of thecombustion ashes together. In the ash melting method to melt the ash,which comprises the step of supplying ash on the inclined floor from oneend of the furnace, melting the supplied ash by a burner, and pushing itforward along the inclined floor towards a drain port provided at a farend of the inclined floor to drain the molten ash, discharging moltenslugs of the ash at the other end of the furnace, this invention ischaracterized by the following features. In the step of supplying ash,it further comprises the step of supplying the primary ash (ashcontaining rough particles) from the upper end of the furnace to form anupper layer of a two-tiered layer of ash, supplying the fly ash (ashcontaining minute particles) from the upper end of the furnace to form alower layer of the two-tiered layer of ash, moving the two-tiered layertogether towards the far end of the furnace, and heating and melting thetwo-tiered layer by a burner to form the molten slugs during the movingstep.

In order to melt the ashes as mentioned above, this invention disclosesthe ash-melting furnace to perform efficiently as follows. In theash-melting furnace which comprises an ash supply port to supply ashprovided at one end of the furnace; a slug discharge port to dischargethe molten slugs of the ash at the other end of the furnace; a burner tomelt the ash supplied from the ash supply port, the supplied ash beingpushed forward along an inclined floor towards a drain port provided ata far end of the inclined floor to drain the molten slug, thisash-melting furnace is characterized by the following features. Itcomprises at least two sets of ash supply ports to supply ash providedat an upper end of the furnace, the first ash supply port being used forsupplying the primary ash, the second ash supply port being used forsupplying the fly ash (ash containing minute particles), the primary andfly ash forming a two-tiered layer of ash on an inclined floor, thefirst and second ash supply ports being arranged in such a way that thefly ash forms a lower layer of the two-tiered layer, and the primary ashforms an upper layer on the lower layer of fly ash.

The first ash supply port used for supplying the primary ash can belocated at a downstream area of the furnace, and the second ash supplyport used for supplying the fly ash can be located at an upstream areaof the furnace, respectively. The first ash supply port used forsupplying the primary ash alternatively can be located at an upper areaabove the floor of the furnace, and the second ash supply port used forsupplying the fly ash can be located at a lower area above the floor ofthe furnace.

This invention further comprises an ash feeding means, such as a screwfeeder, to feed the fly ash at an upstream area of said furnace, the ashfeeding means being oriented lengthwise along the inclined floor fromthe ash supply port.

This invention further comprises a gate along the wall of the ash supplyport in order to adjust the height of the layer of ash on the inclinedfloor.

With this embodiment, then, a lower layer of fly ash is formed with alayer of primary ash on top of it. This results in a two-tiered layer ofash in the furnace, with the fly ash completely covered by primary ash.The proportions of the two types of ash in this layer can easily beadjusted, so the minute particles of fly ash are not directly exposed tothe exhaust gases from the burner. This eliminates the problem of thegreater part of the fly ash escaping to the exterior with the exhaustgases. Further, the fly ash is melted smoothly by the heat conductivelytransferred from the primary ash and by the heat directly transferredfrom the molten ash.

Since the inlet for the primary ash is placed further forward on thefurnace and the inlet for the fly ash is placed just behind it, theprimary ash is deposited as a top layer, and the fly ash is depositedbelow the primary ash. A reliable two-tiered layer is, therefore, formedin which the primary and fly ash are clearly segregated.

The inlet for the primary ash is arranged vertically above the near endof the floor of the furnace. Therefore the fly ash is disposedlongitudinally along the inclined surface of the floor. Thus a layer offly ash can be formed which has no irregularities or bends to obstructthe flow of particles. Such a layer can flow steadily withoutexperiencing undulations. Because the primary ash, which consists ofcoarser particles, is deposited atop the fly ash, an upper layer flow isgenerated in the upper portion of the relatively smooth layer of fly ashon the floor of the furnace. This creates a well-defined two-tieredlayer in which the primary and fly ash are clearly separated.

With this configuration mentioned above, there may be someirregularities or bends in the ash-supplying path for the primary ash atthe contact area with the fly ash layer. However, because the primaryash consists of coarser particles, there will be no trouble for the ashlayer to flow smoothly.

Because several screw feeders are provided in at least one location,namely the inlet for the fly ash, as the feeding means to force feed thefly ash from outside of the furnace, the fly ash can flow in stablefashion. As a result, this ensures that the two-tiered layer will formin a stable fashion. The amount of fly ash in the two-tiered flow can beadjusted to provide an appropriate proportion of primary to fly ash.This allows the supply of an amount of fly ash such that the primary ashenclosing the fly ash will reliably melt.

Because a gate is provided to adjust the height of the partition whichdetermines the quantity of ash to be supplied to the inlet for theprimary ash, it is easy to adjust the proportions of primary and fly ashin the mixture. By adjusting the angle of repose for each type ofprimary ash, the operator can assure that the leading end of the layerof primary ash ends up an appropriate distance from the discharge port.This will result in a stable flow of molten ash consisting of primaryand fly ash.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a rough block diagram of a system to control combustion in anash-melting furnace which is a first preferred embodiment of thisinvention.

FIG. 2 is an enlarged view to show discharging the molten slug from thedrain port taken along line II—II shown in FIG. 1.

FIGS. 3 are diagrams of the control operations shown in FIG. 1.

FIGS. 4 show plan views of the slug reservoir at the downstream end ofthe furnace according to preferred embodiments of this invention. FIG.4(A) shows a slug reservoir of triangular form; FIG. 4(B) shows a slugreservoir of parabolic form, and FIG. 4(C) shows a slug reservoir offunnel-shaped form.

FIG. 5 shows an enlarged view taken along line II—II in FIG. 1 whichcorresponds to FIGS. 4.

FIG. 6 shows a cross section taken along line Z—Z in FIG. 5, which is avertical cross section of the slug reservoir.

FIG. 7 is a diagram showing one form of a contacting surface of apusher, and a movement of the ash layer according to a preferredembodiment of this invention.

FIG. 8 is another diagram showing a form of a contacting surface of apusher, and the movement of the ash layer according to another preferredembodiment of this invention.

FIG. 9(A) is a diagram showing a form of a contacting surface of apusher, and the movement of the ash layer according to yet anotherpreferred embodiment of this invention, and

FIG. 9(B) is a modification of the embodiment shown in FIG. 9(A).

FIGS. 10 show another embodiment of the pusher shown in FIG. 8. FIG.10(A) shows a semicircular contacting surface, and FIG. 10(B) shows aparabolic contacting surface.

FIG. 11 is a rough block diagram of an ash-melting furnace according toa preferred embodiment of this invention which comprises a screw feeder.

FIG. 12 is another rough block diagram of an ash-melting furnaceaccording to another preferred embodiment of this invention whichcomprises a screw feeder.

FIG. 13 is a rough block diagram of an ash-melting furnace according toa preferred embodiment of this invention which comprises a screw feederand a gate.

FIG. 14 is a rough block diagram of an ash-melting furnace according toa preferred embodiment of this invention which comprises a plurality ofscrew feeders and a gate.

FIG. 15 is an ash-melting furnace for mixing and melting the primary ashand fly ash according to a preferred embodiment of this invention.

FIG. 16 is a rough block diagram of an ash-melting furnace as shown inFIG. 15 but which has a gate at the supply port for the primary ashaccording to another preferred embodiment of this invention.

FIG. 17 is a rough block diagram of an ash-melting furnace which hasscrew feeders for the primary ash and the fly ash, respectively,according to another preferred embodiment of this invention.

FIG. 18 is a rough block diagram of an ash-melting furnace as shown inFIG. 17 but which has a gate for the primary ash according to anotherpreferred embodiment of this invention.

FIG. 19 is a rough block diagram of an ash-melting furnace according tothe related art.

FIG. 20 is another rough block diagram of an ash-melting furnace whichhas a gate at the ash supply port according to the related art.

FIG. 21 is a plan view rough block diagram of an ash-melting furnacewhich has a dike at a slug reservoir and a drain port according to therelated art.

FIG. 22(A) is a plan view rough block diagram of the pusher, and

FIG. 22(B) is a cross section taken along line B—B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In this section, a detailed explanation of the invention will be givenwith reference to the drawings. To the extent that the dimensions,materials, shape and relative position of the components described inthese embodiments need not be definitely fixed, the scope of theinvention is not limited to the embodiments as described herein, whichare meant to serve merely as examples.

FIG. 1 is a block diagram of a system to control combustion in anash-melting furnace which is a first preferred embodiment of thisinvention.

The ash-melting furnace of this invention has, at one end of the furnacebody, an ash supply unit 53 with an ash supply port 54 below it. Ash 50is supplied via the supply port 54 and deposited on floor 55 directlybelow the port. Pushed forward by pusher 58, the supply device, the ashforms a layer 59 along inclined floor 55 as it travels towards the farend of the floor. The ash on the surface of the layer 59 is heated andmelted by oxygen-enriched burner 10, which is installed on the centerline of ceiling 56 on the top of the furnace body. The resulting moltenash 25 flows through slug drain port 20 at the far end of floor 55towards discharge port 57 in the form of molten slugs 25 a. In theserespects the current invention does not differ from the related artapparatus discussed above.

In this embodiment, infrared CCD camera 15 or some other industrial CCDcamera which can measure temperature distribution is installed on thefar end of the furnace body so that it can monitor the state of flow ofthe molten slugs 25 a which drip from drain port 20. Combustion controldevice 14 controls the quantity of ash supplied and the quantity of heatproduced by the burner in response to the state of flow of the moltenash.

The oxygen-enriched burner 10 is supplied with fuel from oil tank 11 a,the fuel source, via valve FIC-11, which controls the volume of flow.Oxygen is added to the compressed air supplied from source 12 a (an airblower) via valve FIC-12, which controls the volume of flow. The oxygenis drawn from oxygen source 13 a (an oxygen generator PSA or an oxygencylinder) and supplied via valve FIC-13, which controls the volume offlow. In this way the e required concentration of oxygen (25 to 40%) canbe achieved in the oxygenated air supplied to the burner.

Valves FIC-11, FIC-12 and FIC-13 are each actuated remotely on receiptof a signal from the combustion control device 14.

Ash supply control unit 19 controls the range of motion (i.e., thelinear travel) of pusher 58 so as to control the quantity of ashsupplied.

A screw feeder, which will be shown in a subsequent embodiment, may beused as the pusher 58. In this case ash supply control unit 19 wouldcontrol the rotary speed of the feeder.

The combustion control device 14 comprises infrared CCD camera 15; imageprocessing unit 16, which processes the images obtain ed by camera 15,including producing, eliminating, synthesizing and comparing images;calculation unit 17, which, using the data obtained from the processingunit 16, performs required control operations which will be discussedshortly; and control unit 18, which, based on the result of the controloperations, outputs signals to optimally control the operation of thevalves FIC-11, FIC-12 and FIC-13, as well as the operation of unit 19,which governs the quantity of ash supplied. Commands from control unit18 respectively actuate the valves FIC-11, FIC-12 and FIC-13 and the ashsupply control unit 19.

The infrared camera or other industrial CCD camera 15 can detecttemperature distribution. The standard value is calculated by thecomparison between width y, the width of the slug at a predetermineddistance from the drain, and the width Y of the drain, and the relevantdata for the control is obtained using the standard value each time. Thetemperature of the slug is detected based on a color signal.

The order of control operations in this embodiment will next beexplained with reference to FIGS. 3.

As can be seen in FIG. 3(1), the temperature of molten slug 25 a isobtained from infrared CCD camera 15. This value is compared with a setvalue (i.e., a standard value). When it is detected that the temperatureis above a given value, the quantity of oxygen or fuel is adjusted sothat the temperature of the slug regains its set value.

As is shown in FIG. 3(2), the surface area of molten slug 25 a isobtained by integration processing. Its volume of flow is detected byobserving the changes in its surface area over time. Each value iscompared with a set value for surface area. If there is no variation inthe temperature of the slug, the quantity of ash supplied is adjusted.If the temperature of the slug should vary, the control measuresdescribed in FIG. 3(1) above are implemented to adjust the temperaturewithin the furnace and that of the slug. In this way the slug's volumeof flow is brought back to the prescribed value.

As can be seen in FIG. 3(3), the displacement L of the slug is detectedover scan time t and used to obtain the velocity of the slug's flow.This value is compared with a set value. When it is detected that thevelocity of the flow has exceeded a given value, the measures describedin FIG. 3(1) and FIG. 3(2) above are implemented to adjust the volume ofoxygen added to the air and/or the quantity of fuel or ash supplied. Inthis way the slug's velocity of flow is brought back to the prescribedvalue.

The foregoing control measures also counteract fluctuations in the loadimposed by molten slugs 25 a (i.e., changes in ash quality) and therebyallow the slugs to drain in a more stable fashion.

The addition of oxygen to the air as described above allows theoxygenated air used in burner 10 to have the appropriate concentrationof oxygen. This allows a higher combustion temperature to be used thanwas the case with related art burners and assures stable discharge ofthe molten slugs 25 a.

In contrast to the way heating was controlled in related art airburners, in this invention it is controlled by the addition of oxygen.This allows the burner to function with a smaller volume of air andrequires less nitrogen in the furnace. The results are less thermal NOxand less exhaust gas, which translate into a reduction of equipment andoperating costs to process exhaust gas.

In this embodiment, if the temperature of the slug is appropriate, itsvolume of flow can be controlled by adjusting the quantity of ashsupplied, and its temperature and flow velocity can be controlled byadjusting the quantity of heat produced by the burner to an appropriatevalue.

The quantity of heat produced by the burner can be adjusted bycorrecting the volume of fuel supplied to the burner, the volume of airsupplied for combustion or the volume of oxygen added to that air. Whenthis is compared with the method used to adjust the heat in the relatedart, namely to increase the quantity of fuel or the volume of air usedfor combustion, we see that increasing the volume of oxygen added to theair (and so decreasing the volume of nitrogen) has the effect ofreducing the volume of gas and raising the temperature of the exhaustgases. Thus a smaller volume of exhaust gases will be released, and theflame of the burner will have a higher temperature. Load fluctuationscan be addressed promptly, resulting in more stable and efficientoperation.

Since properly adjusting the volume of oxygen to be added to the air hasthe result of reducing the volume of nitrogen which goes into thefurnace, it follows that a smaller volume of thermal NOx will bereleased.

When the volume of exhaust gas is reduced, preheaters, dust eliminatorsand equipment used to treat exhaust gas in order to eliminate NOx can bemade smaller, saving space in the plant or reducing its size as well.

In this embodiment, if the detected temperature of the slug isappropriate, its volume of flow as calculated from the surface area ofthe flow per unit of time can be adjusted by controlling the quantity ofheat produced by the burner.

The heat produced by the oxygen-enriched burner is controlled byadjusting the quantity of fuel supplied to the burner, the volume ofcompressed air used to induce combustion, or the volume of oxygen addedto this air. Thus a smaller volume of gas is required, and thetemperature of the combustion gases will increase rapidly. Less exhaustgas will be released and the temperature of the flame can be increasedquickly. This allows combustion to be induced more efficiently.

FIG. 1 shows the basic configuration of an ash-melting furnace accordingto this invention. In this ash-melting furnace, ash supply unit 53 is onone end of the main body of the furnace, and supply port 54 is directlybelow it. The ash 50 is supplied via supply port 54 and deposited onfloor 55 under the supply port. A layer of ash 59 is created alonginclined floor 55 and made to move towards the far end of the floor.Oxygen-enriched burner 10, which is installed on the center line ofceiling 56 on top of the furnace body, heats and melts the ash on thesurface of ash layer 59. The resulting molten ash 25 accumulates asmolten slug in reservoir 65, which is created by dike 23, a structure atthe far end of the floor 55. The accumulated molten slug 25 a passesthrough drain port 20, which is in the center of the dike 23, and exitsthrough discharge port 57.

FIGS. 4 through FIG. 6 show the shapes of the floors in severalash-melting furnaces which are other preferred embodiments of thisinvention. They are designed to assure that the molten slug on the floorof the furnace will have high fluidity during its passage towards thedischarge port and to improve the speed at which it will be discharged.

The slug reservoir 65 is shown in FIG. 4(A), 4(B) and 4(C). In each caseit is almost funnel-shaped and leads to drain port 20, which is placedalong the center line Y—Y of dike 23 at the far end of floor 55. Thisreservoir may be triangular, like reservoir 65 a, parabolic, likereservoir 65 b, or funnel-shaped, like reservoir 65 c. In theseexamples, the lateral guide walls of dike 23 may be straight, likesurfaces 66 a, curved, like surfaces 66 b, or funnel-shaped, likesurfaces 66 c. The width of the inflow of molten slug towards drain port20 is gradually narrowed by the continuous surfaces 66 a, 66 b and 66 c.In this way the flow of the slug is naturally made to converge towardsdrain port 20.

The configuration of the slug reservoir 65 is shown in greater detail inFIG. 5 and FIG. 6. FIG. 5 shows the shape of the floor of reservoir 45in a cross section which is orthogonal to the direction of flow. Thefloor is recessed like the bottom of a ship in such a way that thedeepest part runs along the center line Z—Z of reservoir 65. Alongcenter line Z—Z in its longitudinal direction (the direction of flow),floor 24 (shown by angled lines) slopes gradually downward from upstreamto downstream. The effect of this inclined, ship bottom-shaped floor 24is to cause the flow of molten slug 25 a to converge towards the centerline Z—Z of drain port 20.

The notch of the drain port 20 may also be shaped like the bottom of aship (i.e., it may be a flattened “V”), so that the molten slug willmove smoothly while passing through the drain.

In this embodiment, the ash melted by the heat from the burner is madeto move towards the drain, which is the outlet of the slug reservoir,without being collected in a specially constructed reservoir unit andwithout leaving unburned sediment behind. The molten ash is efficientlydirected towards the slug drain port so that it can be dischargedsmoothly. The slug flows more rapidly and has less contact with thefloor of the furnace and less surface area. As a result, it experiencesless thermal loss.

The slug reservoir is shaped like a funnel from its entry to its drain.Because the two corners on the sides of the dike have been eliminated,the unburned sediment which collected there has also been eliminated.The flow of molten slug is now concentrated naturally towards the drain.The flow velocity in the streamlined reservoir towards the dike isslower than in related art reservoirs. As a result, the heat-resistantmaterials near the dike experience less high-temperature corrosion.

The drain is placed directly in the center of the dike, and the ash ismelted by heat from a burner installed along the center line of thefurnace body. This design assures that the central portion of the moltenash will flow smoothly along the center line of the floor.

The end of the floor inclines somewhat downward along its center line toform a concavity. This assures that the flow of molten ash towards thedrain can be directed and concentrated in the direction of the draineven from locations distant from the drain.

Next, several improvements in the shape of the end of the pusher in thedevice to push the ash are shown in FIG. 7 through FIGS. 10.

FIG. 7 and FIG. 8 show the shapes of the contacting portions of twopushers and illustrate how the ash is supplied by the said pushers tothe portion of the furnace which contains the region covered by theradiant heat of the burner.

As can be seen in FIG. 7, pushing element 58 b at the end of the pusherin the first embodiment is narrower at its base than the overall widthof floor 55. The central portion of its end is flat, and its sidesgradually widen from front to back. To be more specific, its frontsurface is orthogonal to the direction of flow. Its overall shape fromfront to back is that of a pedestal with a flat top. Its sides areslightly curved and incline at a steep reverse angle. Thus the clumps ofash pushed forward by pushing element 58 b as it moves back and forth inan appropriate range of motion, as shown by the arrows, form an ashlayer 59 a whose leading end narrows as it advances. This ash layermoves towards heated region 35 a, which is in the vicinity of the regioncovered by the heat radiating from the flame of burner 10. If the widthS of the end of the pushing element and the position where the end ofpushing element 58 b comes to rest are selected appropriately, the ashto be melted can be supplied efficiently to the region 35 of radiantheat, and the quantity of ash supplied to the unheated portion of thefurnace can be minimized.

FIG. 8 shows the shape of the pushing element in a second embodiment ofthe pusher and the movement of the ash layer formed by the pushingelement.

As can be seen in FIG. 8, the pushing element 58 c of this pusher isformed of a material whose width is close to that of floor 55. Itscenter is indented to form a concave pushing surface 58 c ₁. The pushingforce generated by surface 58 c ₁ is primarily directed towards thecenter line to form ash layer 59 b.

Thus the ash can be directed towards the center of the region of radiantheat 35, which is on the center line of the furnace. The concave pushingsurface may be semicircular, as shown in FIG. 10(A), or it may beparabolic, as shown in FIG. 10(B).

If its center is shaped like a pedestal and extends forward, and itssides are raked back at a steep angle, the advancing pusher will leavebehind the ash on either side which is outside of the heated regioncontaining the area covered by radiant heat from the burner in thecenter of the furnace. When the pusher advances, the ash in front of itscentral portion will be pushed forward, but the ash on either side ofits backwardly inclined surfaces will be left behind. This design makesit possible to supply ash only to the center of the furnace.

FIG. 9(A) shows the shape of the pushing element in a pusher which is athird embodiment of pusher and the movement of the ash layer created bythis pushing element.

As is shown in the embodiment, the pushing element 58 d in the pusher ofthe third embodiment is formed of a material whose width is close tothat of floor 55 and whose cross section protrudes upward in the center.This raised area in the center of the pusher supplies more ash than thelower portions on either side to create an ash layer 59 which is higherin the center. This design allows a sufficient quantity of ash to besupplied to heated region 35 a, which receives a great deal of heat.

This pusher may also have a pushing element 58 e as shown in FIG. 9(B),with a raised portion whose sides slope downward to form a gentler ashsupply surface.

A pusher whose front end is configured as in this embodiment is quitedifferent from pushers of the related art, which had a rectangular crosssection and which pushed a uniform quantity of ash all across theirwidth. The new design allows a larger quantity of ash to be pushedtowards the center of the furnace. This maximizes the quantity of ashsupplied to the center and minimizes the quantity supplied to eitherside.

If the end of the pusher has its sides furthest forward with the surfacedropping away towards the center to form a concave pushing surface, theash pushed by the pushing surface will be directed towards the centerline which passes through the middle of the region of radiant heat. Thisdesign has the effect of maximizing the quantity of ash delivered to thecenter of the furnace and minimizing the quantity delivered to eitherside.

The embodiments illustrated in FIG. 11 through FIG. 14 show ash-meltingfurnaces from which the drainage of molten ash is stable with littlefluctuation. In the ash melting furnace 100, as can be seen in FIG. 11,the feeding means to feed the ash on the inlet side of the floor is nota pusher but a screw feeder 71 which can continuously feed the ash. Suchscrew feeders are provided in at least two places along the width offloor 55. They feed the ash along the inclined surface of floor 55.

The rotary speed of the screw feeders 71 can be varied to feed anappropriate quantity of ash with respect to the kind of ash being meltedand its position in the furnace.

With this configuration, ash layer 59 will advance in a stable fashion,and its surface will receive a constant quantity of radiant heat fromburner 10. This will produce a stable drainage of molten ash 25.

FIG. 12 is a different embodiment from that shown in FIG. 11. Theash-melting furnace 100 in FIG. 12 has, in addition to screw feeders 71,the feeding means to continuously feed ash along floor 55, a second setof continuous feed devices, screw feeders 72, in the ash supply unit 53.

In other words, in addition to the screw feeders 71 which are orientedlengthwise along the floor 55 from the inlet, this embodiment hasseveral screw feeders 72, which are oriented vertically above the inlet.There are more than one of each type of screw feeder. Screw feeders 71are arranged in a row across the width of the floor, and screw feeders72 are arranged in a row across the width of the stack. These feedersmake it possible to supply ash 50 continuously to the highest part ofthe floor and to advance the ash 50 continuously along floor 55 towardsdischarge port 57.

Screw feeders 71 and 72 may have adjustable speed of rotation, or ahelical ribbon screw feeder may be used as feeder 72.

With this sort of configuration, the cross-linkages which graduallydeveloped in the ash which was gravity-fed from stack 70 to the floor ofrelated art furnaces do not occur. A constant, uniform supply of ash isdelivered to the inlet of the furnace, creating a stable moving layer ofash 59. The surface of this layer receives a constant quantity ofradiant heat from burner 10, enabling molten ash 25 to drain in a stablefashion.

Like the embodiment in FIG. 11, the embodiment in FIG. 13 has as itsfeeding means to feed ash a screw feeder 71 which can continuously feedthe ash longitudinally down the floor from the inlet of the furnace. Inaddition, it has a gate 74 at the supply port 54 which can be raised orlowered to adjust the height H at which the supply of ash is cut off.The lowest position of gate 74 must be one which will not allow it tointerfere with the operation of screw feeder 71.

With the above configuration, using screw feeder 71 as the feeding meansto continuously feed ash 50 along floor 55 creates a stable ash layer59. Using the screw feeder together with a gate 74 on supply port 54 toadjust the height H at which supply unit 53 is partitioned allows theangle of repose γ of the ash layer to be adjusted by the gate 74. Theneven though different types of ash may be melted, a stable moving layerof ash 59 can still be created, and a stable drainage of molten ash 25can be effected.

FIG. 14 shows another embodiment of the device pictured in FIG. 13. Thisfurnace has a screw feeder 71 running along the floor 55 and a verticalgate 74 which can be raised and lowered to adjust the height H at whichsupply unit 53 is partitioned. In addition, it has a vertical screwfeeder 72 in the supply unit 53.

In addition to the effects of the configuration shown above in FIG. 13,this configuration has the effect of preventing cross-linkages fromoccurring in stack 70 and assuring a smooth supply of ash 50 to floor55.

With this embodiment, the ash delivered via the supply port onto thefloor of the furnace is continuously pushed forward along the floor bythe feeding device. Thus the layer of ash created on the inclinedsurface of the floor will travel forward in a stable fashion withoutexperiencing undulation. It will be in a uniform state, and its surfacewill receive a constant quantity of radiant heat from burner 10. Thiswill produce a stable drainage of molten ash 25. Because the feedingdevice is a screw feeder, the ash can be supplied continuously or invarying amounts. This allows the system to respond effectively to loadfluctuations due to the type and condition of the ash used.

Screw feeders are provided to supply the ash both from the supply portto the near end of the furnace floor and from there down the floor tothe far end. These feeders allow the quantity of ash supplied to bevaried across the width of the furnace. More specifically, they allowheating disparities across the width of the furnace which are due to theposition of the burner to be addressed by increasing or decreasing thequantity of ash being fed. This allows the state of melting to beequalized across the furnace.

A feeding means to continuously feed the ash along the floor will createa stable ash layer. If a gate is also provided at the supply port tochange the height of the partition which forms the supply unit, it canbe used to control the angle of repose of the ash layer. This willassure a stable drainage even when ash of different types is beingmelted.

FIG. 15 through FIG. 18 show a number of embodiments of an ash-meltingfurnace in which primary and fly ash are combined before they aremelted.

As can be seen in FIG. 15, the ash-melting furnace 100 of thisembodiment comprises primary ash supply unit 531, which includes supplyport 531 a, an inlet on the near end of the furnace body above inclinedfloor 55; fly ash supply unit 531, which includes a supply port 532 ajust behind port 531 a; pusher 58, the feeding means to feed the ash,which travels along floor 55 below supply port 532 a; discharge port 57,the outlet for molten ash 25 on the far end of the furnace body; andburner 10, which is installed on ceiling 56 of the furnace body.

With the configuration described above, fly ash 502 and primary ash 501are supplied separately via two supply ports which are placed one infront of the other. Fly ash 502 falls naturally to the inlet to floor 55and is fed along the floor by pusher 58 to form fly ash layer 502 a. Asthe layer 502 a is formed, the primary ash 501 which is above it fallsnaturally from supply port 531 a. As fly ash layer 502 a flows forward,primary ash layer 501 a is formed on top of it. The two layers movetogether towards the far end of floor 55.

As the combined layer of ash travels towards the far end of floor 55,the radiant heat from the flame of burner 10 heats and melts the surfaceof primary ash 501 in layer 501 a. The fly ash 502 in the lower layer isnot exposed directly to the flame of burner 10, nor is it conveyedupward by the combustion gases. Rather, it is heated and melted by theheat conductively transferred from primary ash 501 and by the heatdirectly transferred from molten ash 25.

Primary ash 501 and fly ash 502 are heated together until they formmolten ash 25. They pass through discharge port 57 as slugs, drip onto awater-sealing conveyor below the port, and are discharged to theexterior.

With the configuration described above, the surface of primary ash layer501 a in the vicinity of supply port 531 a will experience sinteringfrom the radiant heat of the flame of burner 10. A crusher (not shown)may be provided which can move up and down to break up this sinteredlayer.

The device shown in FIG. 16 is a variant of the embodiment in FIG. 15. Agate is provided on the supply port for the primary ash in the furnaceshown in FIG. 15 which can adjust the angle of repose of the primary ashand the mixture of the primary and fly ash.

As can be seen in FIG. 16, the ash-melting furnace 100 of thisembodiment comprises primary ash supply unit 531, which includes supplyport 531 a, an inlet on the near end of the furnace body above inclinedfloor 55; fly ash supply unit 531, which includes a supply port 532 ajust behind port 531 a; pusher 58, the feeding means to feed the ash,which travels along floor 55 below supply port 532 a; discharge port 57,the outlet for molten ash 25 on the far end of the furnace body; burner10, which is installed on ceiling 56 of the furnace body; and gate 74,which can be raised or lowered to adjust the height H of the partitionon the primary ash supply port 531 a.

Such a vertical gate 74, which is interlocked with pusher 58, can beraised or lowered via mechanism 74 a to adjust the height H of thepartition which admits primary ash 501 when different types of ash areto be melted. This allows the proportions of the primary ash 501 and flyash 502 to be adjusted when layers 501 a and 502 a are combined. It alsoallows the leading end of primary ash layer 501 a to end up anappropriate distance from the discharge port 57 so that a stable flow ofmolten ash 25 will drain from the port.

In this embodiment, a layer of primary ash 501 a which is optimal formelting can be formed by adjusting the layer in response to a change inits angle of repose. This is done by adjusting gate 74 so that theheight H of the partition admitting primary ash 501 is set at theappropriate level, and it optimizes the proportions of primary ash 501and fly ash 502 in the mixture. In this way the primary and fly ash canbe melted together to produce a stable molten ash and a stable drainage.

FIG. 17 shows another embodiment in which screw feeders are provided tosupply both the primary and fly ash.

As can be seen in FIG. 17, an adjustable-speed screw feeder 72 ispositioned vertically along the path by which the primary ash issupplied in supply unit 531. Another adjustable-speed screw feeder 71 isoriented longitudinally in supply unit 535 along the inclined surface offloor 55 on the inlet side of the furnace.

With the configuration described above, fly ash 502 and primary ash 501are supplied via two separate supply units, 531 and 535, and they arefed into the furnace by screw feeders 72 and 71. The fly ash 502 is fedalong floor 55 by screw feeder 71 to form fly ash layer 502 a. As layer502 a is formed, the primary ash 501 above it is fed into the furnacefrom supply unit 531 by screw feeder 72 to form primary ash layer 501 aon top of the moving layer of fly ash 502 a. Thus a two-tiered layer ofash is formed on floor 55 and in that state transported to the far endof floor 55.

As the combined layer of ash which is described above travels towardsthe far end of floor 55, the radiant heat from the flame of burner 10heats and melts the surface of primary ash 501 in layer 501 a. The flyash 502 in the lower layer is not exposed directly to the flame ofburner 10, nor is it conveyed upward by the combustion gases. Rather, itis heated and melted by the heat conductively transferred from primaryash 501 and by the heat directly transferred from molten ash 25, just asin the previous embodiment.

In this embodiment, adjustable-speed screw feeders 72 and 71 areprovided in supply units 531 and 535, respectively. The rotary speed ofthese screw feeders can be adjusted to provide a continuous supply ofash. This will allow a stable layer of ash to form and assure a stablemelting process. It also allows the amounts of primary and fly ash to beeasily adjusted.

FIG. 18 shows the configuration of a fourth preferred embodiment of thisinvention. Here a gate to adjust the angle of repose of the ash andalter the proportions in which the primary and fly ash are combined isadded to the previous embodiment in which screw feeders are provided inthe supply units for both the primary and fly ash.

As can be seen in the drawing, an adjustable-speed screw feeder 72 ispositioned vertically in the supply unit 531. Another adjustable-speedscrew feeder 71 is provided along the inclined surface of floor 55 inthe supply unit 535. A vertical gate 74 which can be raised and loweredis provided in supply unit 531 a to adjust the height H at which thesupply unit is partitioned.

With this configuration, a two-tiered layer of ash is formed on floor 55with fly ash 502 on the bottom and primary ash 501 on top. Since themethod by which this two-tiered layer is transported intact to the farend of floor 55 is the same as that employed in the third embodiment, adetailed discussion of it is unnecessary. In this embodiment, the gate74, which is interlocked with screw feeders 72 and 71, can be adjustedvia mechanism 74 a to change the height H of the partition to respond todifferent types of primary ash 501. This also adjusts the proportion inwhich the primary ash 501 and the fly ash 502 are supplied and allowsthe leading end of primary ash layer 501 a to end up an appropriatedistance from the discharge port 57 so that a stable flow of molten ash25 will drain from the port. The speed of adjustable-speed screw feeders72 and 71 in supply units 531 and 535 can be adjusted, and the height Hof the partition on supply port 531 a can be adjusted by gate 74, toeasily control the amount of primary ash 501 and fly ash 502 supplied.Adjusting the angle of repose, the angle at which the ash is supplied,enables the furnace to respond to different types of ash.

With this embodiment, then, a lower layer of fly ash is formed with alayer of primary ash on top of it. This results in a two-tiered layer ofash in the furnace, with the fly ash completely covered by primary ash.The proportions of the two types of ash in this layer can easily beadjusted, so the minute particles of fly ash are not directly exposed tothe exhaust gases from the burner. This eliminates the problem of thegreater part of the fly ash escaping to the exterior with the exhaustgases.

Further, the fly ash is melted smoothly by the heat conductivelytransferred from the primary ash and by the heat directly transferredfrom the molten ash.

Since the inlet for the primary ash is placed further forward on thefurnace, and the inlet for the fly ash is placed just behind it, theprimary ash is deposited on top of the fly ash. A reliable two-tieredlayer is formed in which the primary and fly ash are clearly segregated.

The inlet for the primary ash is oriented vertically above the near endof the floor of the furnace. That for the fly ash is orientedlongitudinally along the inclined surface of the floor. Thus a layer offly ash can be formed which has no irregularities to obstruct the flowof particles. Such a layer can flow steadily without experiencingundulations.

Because the primary ash, which consists of coarser particles, isdeposited atop the fly ash, an upper layer flow is generated in theupper portion of the relatively smooth layer of fly ash on the floor ofthe furnace. This creates a well-defined two-tiered layer in which theprimary and fly ash are clearly separated.

Because several screw feeders are provided in at least one location, theinlet for the fly ash, as the feeding means to feed the ash into thefurnace, the amount of fly ash in the two-tiered flow can be adjusted toprovide an appropriate proportion of primary to fly ash. This allows thesupply of an amount of fly ash such that the primary ash enclosing thefly ash will reliably melt.

Because a gate is provided to adjust the height of the partition whichdetermines the quantity of ash to be supplied to the inlet for theprimary ash, it is easy to adjust the proportions of primary and fly ashin the mixture. By adjusting the angle of repose for each type ofprimary ash, the operator can assure that the leading end of the layerof primary ash ends up an appropriate distance from the discharge port.This will result in a stable flow of molten ash consisting of primaryand fly ash.

The invention according to claims 1 and 2 provides an ash-meltingfurnace which can counteract fluctuations in the load and so allow theslugs to drain in a stable fashion. It also can control the heating bythe burner in accordance with the discharging state of the slugs.

The invention according to claims 3 through 5 provides an ash-meltingfurnace which can enhance the efficiency of discharging the moltenslugs. This invention can efficiently discharge specially the moltenslugs which are collected in slug reservoir being formed from the moltenash, and so enhance the discharging speed of the molten slugs.

The invention according to claims 6 through 8 discloses a unique form ofthe pushing element of the pusher which can push the ash along the floortowards the discharge port forming the ash layer. This pusher canefficiently minimize pushing of the ash out of the heating region of theradiated flame including the radiant region, and thus minimize theunheated ash.

The invention according to claims 9 through 11 provides an ash-meltingfurnace which enables a continuous stable supply of ash from the supplyport towards the discharge port to assure a stable outflow of molten ashwith minimum fluctuation.

The invention according to claims 12 through 17 discloses an ash-meltingfurnace to melt the mixture of primary ash and fly ash. This ash-meltingfurnace can prevent the fly ash from dispersing in the atmosphere uponheating, and enable efficient melting of the fly ash with the primaryash.

What is claimed is:
 1. An ash-melting furnace, comprising: an ash supplyport to supply ash provided at one end of said furnace; a slug dischargeport to discharge molten slugs of the ash at another end of saidfurnace; an oxygen-enriched burner to melt the ash supplied from saidash supply port, the supplied ash being pushed forward along an inclinedfloor towards a drain port provided at a far end of said inclined floorto drain the molten slugs; a detector to detect or calculate a volume ora drain velocity of outflow of the molten slugs; a comparator forcomparing an output value from said detector with a preset value; and acontroller to control either quantity of the ash supplied or quantity ofheat produced by said oxygen-enriched burner in response to a signalfrom said comparator in order to make the outflow of the molten slugsstable and continuous.
 2. An ash-melting furnace, comprising: an ashsupply port to supply ash provided at one end of said furnace; a slugdischarge port to discharge molten slugs of the ash at another end ofsaid furnace; an oxygen-enriched burner to melt the ash supplied fromsaid ash supply port, the supplied ash being pushed forward along aninclined floor towards a drain port provided at a far end of saidinclined floor to drain the molten slugs; a combustion control device,comprising: a monitor to monitor a volume or a drain velocity of outflowof the molten slugs at said drain port; a calculator to calculate acontrol signal, based on a result from comparing said monitored volumeor drain velocity with preset value, either for quantity of the ashsupplied or quantity of heat produced by said oxygen-enriched burner;and a controller to control either the quantity of ash supplied or thequantity of heat produced by said oxygen-enriched burner in response tothe control signal from said calculator.
 3. An ash-melting furnace,comprising: an ash supply port to supply ash provided at one end of saidfurnace; a slug discharge port to discharge molten slugs of the ash atanother end of said furnace; an oxygen-enriched burner to melt the ashsupplied from said ash supply port, the supplied ash being pushedforward along an inclined floor towards a drain port provided at a farend of said inclined floor to drain the molten slugs; and a guide wallon a dike for assuring fluidity of the molten slugs at said drain port,wherein said dike is continually straight or curved and width isgradually narrowed towards said drain port.
 4. An ash-melting furnaceaccording to claim 3, wherein said drain port is provided in a center ofsaid dike, and a floor of a slug reservoir is recessed along anorthogonal direction of slug flow, which slopes gradually downward fromupstream to downstream.
 5. An ash-melting furnace, comprising: an ashsupply port to supply ash provided at one end of said furnace; a slugdischarge port to discharge molten slugs of the ash at another end ofsaid furnace; and a pusher to push the ash on an inclined floor suppliedfrom said ash supply port towards a region covered by radiant heat froma burner for melting the ash, wherein said pusher has a pushing surfaceprovided at an end thereof, and a shape of sides of said pushing surfaceis different from a shape of a central portion of said pushing surfacein order to supply the ash efficiently to the region covered by theradiant heat of said burner, wherein the central portion of said pushingsurface is higher than the sides of said pushing surface, or saidcentral portion is formed flat and the sides have a backwardly inclinedsurface in order to supply the ash efficiently to the region covered bythe radiant heat of said burner.
 6. An ash-melting furnace, comprising:an ash supply port to supply ash provided at one end of said furnace; aslug discharge port to discharge molten slugs of the ash at another endof said furnace; and a pusher to push the ash on an inclined floorsupplied from said ash supply port towards a region covered by radiantheat from a burner for melting the ash, wherein said pusher has apushing surface provided at an end thereof, and a shape sides of saidpushing surface is different from a shape of a central portion of saidpushing surface in order to supply the ash efficiently to the regioncovered by the radiant heat of said burner, wherein the central portionof said pushing surface drops away towards a center of said pusher toform a concave pushing surface, so that said pushing surface is directedtowards a center line which passes through a middle of the region ofradiant heat.
 7. An ash-melting furnace, comprising: an ash supply portto supply ash provided at one end of said furnace; a slug discharge portto discharge molten slugs of the ash at another end of said furnace; aburner to melt the ash supplied from said ash supply port, the suppliedash being pushed forward along an inclined floor towards a drain portprovided at a far end of said inclined floor to drain the molten slugs;and an ash feeder system to continuously feed the ash from said ashsupply port along said inclined floor, said ash feeder system comprisinga first ash feeder oriented lengthwise along said inclined floor fromsaid ash supply port, and a second ash feeder oriented vertically abovesaid ash supply port.
 8. An ash-melting furnace, comprising: an ashsupply port to supply ash provided at one end of said furnace; a slugdischarge port to discharge molten slugs of the ash at another end ofsaid furnace; a burner to melt the ash supplied from said ash supplyport, the supplied ash being pushed forward along an inclined floortowards a drain port provided at a far end of said inclined floor todrain the molten slugs; an ash feeder to continuously feed the ash fromsaid ash supply port along said inclined floor, said feeder beingprovided in said ash supply port; and an adjustable gate along a wall ofsaid ash supply port for adjusting the height of a layer of said ash onsaid inclined floor.
 9. An ash-melting furnace, comprising: at least twoash supply ports to supply ash provided at an upper end of said furnace,the first ash supply port being used for supplying primary ash, thesecond ash supply port being used for supplying fly ash (ash containingminute particles), said primary and fly ash forming a two-tiered layerof ash on an inclined floor, said first and second ash supply portsbeing arranged in such a way that the fly ash forms a lower layer ofsaid two-tiered layer, and the primary ash forms an upper layer on saidlower layer of fly ash; a slug discharge port-to discharge molten slugsof the ash at the other end of said furnace; and a burner to melt thefly and primary ash supplied from said at least two ash supply ports,the supplied ash being pushed forward along said inclined floor towardsa drain port provided at a far end of said inclined floor to drain themolten slug.
 10. An ash-melting furnace according to claim 9, whereinsaid first ash supply port used for supplying the primary ash is locatedat a downstream area of said furnace, and said second ash supply portused for supplying the fly ash is located at an upstream area of saidfurnace.
 11. An ash-melting furnace according to claim 9, wherein saidfirst ash supply port used for supplying the primary ash is located atan upper area above the floor of said furnace, and said second ashsupply port used for supplying the fly ash is located at a lower areaabove the floor of said furnace.
 12. An ash-melting furnace according toclaim 9, further comprising an ash feeding means, such as a screwfeeder, to feed the fly ash at an upstream area of said furnace, saidash feeding means being oriented lengthwise along said inclined floorfrom said ash supply port.
 13. An ash-melting furnace according to claim9, further comprising a gate along a wall of said ash supply port foradjusting the height of a layer of ash on said inclined floor.
 14. Anash melting method to melt ash, comprising a step of: supplying primaryash (ash containing rough particles) from an upper end of said furnaceto form an upper layer of a two-tiered layer of ash; supplying fly ash(ash containing minute particles) from the upper end of said furnace toform a lower layer of the two-tiered layer of ash; moving the two-tieredlayer together towards the far end of said furnace, and heating andmelting said two-tiered layer by a burner to form molten slugs duringsaid moving step; and discharging said molten slugs from a slugdischarging port at the other end of the furnace.